1. Field of the Invention
The present invention relates to high-output semiconductor laser light sources including a high-output semiconductor laser and a sub-mount which are bonded to each other and, more particularly, relates to structures capable of efficiently dissipating heat generated from a semiconductor laser through a sub-mount for improving output characteristics and reliability of a semiconductor laser light source.
2. Description of the Background Art
Semiconductor lasers output laser light and also generate heat during operations. In general, semiconductor lasers exhibit improved output characteristics and improved reliability at lower temperatures and, therefore, it is important to dissipate heat therefrom. As heat sinks for heat dissipation, there have been utilized members made of high-heat-radiation metal materials (for example, Cu). However, such heat sinks made of Cu and the like have linear expansion coefficients larger than semiconductor lasers, which makes it harder to directly bond them to each other. Therefore, in general, a semiconductor laser is bonded to a sub-mount made of a material having a linear expansion coefficient with a value between those of a heat sink and the semiconductor laser, and the sub-mount is bonded to the heat sink.
In such cases, for bonding a semiconductor laser to a sub-mount, there have been structures which place an Au layer on the bonding surface of the semiconductor laser and, further, place an Au/Pt/AuSn solder layer on the sub-mount, for bonding them to each other.
For example, Japanese Patent Application Laid-Open No. 5-190973 (1993) discloses a structure having a semiconductor laser and a sub-mount which are bonded to each other, wherein the sub-mount includes a sub-mount substrate, a Ti layer, a Pt layer and an Au layer which are placed on the sub-mount substrate, and a Pt layer and an AuSn solder layer which have the same length as that of the semiconductor laser and are placed on the upper surface of the Au layer.
For example, Japanese Patent Application Laid-Open No. 2002-359425 discloses a structure having a semiconductor laser and a sub-mount which are bonded to each other, wherein the sub-mount includes a sub-mount substrate, a Ti/Pt layer and an Au layer which are placed on the sub-mount substrate, a barrier layer which has a length smaller than that of the semiconductor laser and is placed on the upper surface of the Au layer, and a solder layer formed to cover the barrier layer.